1. Field of the Invention
The present invention relates to an image forming apparatus, an image forming method and a light amount adjusting method within the apparatus. In the apparatus, a deflecting mirror or a oscillation mirror makes a light beam from a light source scan on an effective image region of a latent image carrier, thereby forming a latent image in the effective image region.
2. Description of the Related Art
In a known apparatus, a deflector deflects a light beam emitted from a light source, the light beam scans on a latent image carrier such as a photosensitive drum and a latent image is formed. In the image forming apparatus described in Japanese Patent Application Laid-Open Gazette No. S63-102545, No. H5-276336 or the like for instance, a semiconductor laser is used as a light source, and the semiconductor laser emits a light beam having a light intensity which corresponds to an image signal. After deflected by a deflector such as a polygon mirror, the light beam modulated in this manner is guided to a latent image carrier via an optical element such as a lens and scans on the latent image carrier along a main scanning direction. As a result, a latent image corresponding to the image signal is formed on the latent image carrier.
Further, in this image forming apparatus, an optical detection sensor such as a photosensor is disposed on a scanning path of the light beam, for the purpose of forming a favorable image. In short, the optical detection sensor detects that the light beam scans passed the starting point of the scanning path, and based on the result of the detection, the timing to start optical modulation is adjusted. In this conventional apparatus, the starting point at which the light beam starts scanning is detected in this manner and a latent image forming operation is accordingly controlled.
In addition, this image forming apparatus comprises an APC circuit to approximately coincide a light amount of the light beam emitted from the semiconductor laser with a reference light amount. The APC circuit compares the reference light amount determined in advance with the amount of the emitted light beam detected by a photo diode built in the semiconductor laser, and controls such that the amount of the light beam coincides with the reference light amount. To be more specific, feeding of an initial pulse which is for activation of the semiconductor laser initiates adjustment of the amount of the light emitted from the semiconductor laser so that the light amount coincides with the reference light amount. This light amount adjusting operation is executed during a period in which the light beam scans one line. When the amount of the emitted light becomes equal to the reference light amount, the light amount adjustment is stopped, and a latent image is formed line by line through light modulation. The light modulation is performed by controlling turning on and off of the semiconductor laser in accordance with the image signal. During this, the amount of the emitted light beam is equal to the reference light amount when the semiconductor laser is ON but zero when the semiconductor laser is OFF.
Upon creation of the latent image for one page, the APC circuit executes the light amount adjustment once again and matches the amount of the light from the semiconductor laser with the reference light amount. After the light amount adjustment is stopped, a latent image for next one page is formed.